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Battery draining

Discussion in 'Scotland' started by Mo younesi, Jan 15, 2020.

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  1. Mo younesi

    Mo younesi Member

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    Hello folks,
    I am coming across a weird electrical problem and really appreciate any advice or if someone have come across this before.
    I changed the battery to a new one last year and has been working fine. A few months later I added a set of fog light and a roof light bar with their own dedicated switches and again everything has been working.
    I also changed the bulb on the instrumentation panel as a few of them were brunt out and lastly the rear wiper motor was gone so replaced that too. Last weekend when I took my 90, 300TDI to work the battery went completely flat. With the help of couple of lads who gave me a push started it and brought it back home. Need to say that I don't drive it every day, once every couple of weeks and most of the time is sitting on the driveway putting up with the rain.
    After taking the battery out and fully charging it (12.6 v on multimeter), started the engine and measured the voltage across battery terminal. Expected to see 14.4v but was reading only 12.2v.
    Tested for any short circuit by disconnecting the negative clamp from the battery and measuring the Amps between the negative terminal and the clamp and get zero amps so guessing that have no short circuit. Rightly or wrongly I concluded that the alternator has had its days. A week later with a brand new 65A alternator fitted also drive belt replaced (even though the old was was good and not extended), I still get the same readings on the multi-meter. Tried a different Multi-Meter and again the same reading. Disconnecting the alternator wires completely and starting the engine on battery, measure the voltage on the alternator (between the big stud for the thick brown cable and the alternator grounded body) and I only get 10.0v.
    Have I bought a faulty alternator? Is there an issue with my engine wiring loom? Anyone have come across this before?
    Really appreciate any advice.
    Thanks,
    Mo
     
  2. steve2286w

    steve2286w Well-Known Member

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    I think Halfords do a free battery check , when charged up it should be higher than 12.6
    Is alternator earthed properly
     
  3. Mo younesi

    Mo younesi Member

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    Thank you Steve for your reply. The battery is relatively new and I have a digital charger that check the state of health of the battery also shows the % charge so I am confident is not the battery. Alternator is brand new from BEARMARCH (AMR4249), so I am confident that that is fine too.
    Someone suggested in the conversation that it might be the voltage regulator which I don't know where is it and what it looks like so I am going to go and find out about that.
     
  4. Disco1BFG

    Disco1BFG Well-Known Member

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    Post some pics of the rear of the alt - so we can see the wiring - it sounds like the alt is DOA, which does happen :rolleyes::( the parts lottery has dealt you a duff one, probably ....

    Voltage decreasing when not running is probably a diode in the rectifier gone open circuit, rather than the regulator which should only affect charging voltage.....both are internal to the alternator...and are available on the bay for very little money if you've the confidence to change them...

    For complete units, I use this lot - no affiliation, just a satisfied customer.

    www.startermotor-alternator.co.uk
     
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  5. steve2286w

    steve2286w Well-Known Member

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    try the voltage check but earth to battery rather than alt body , I had charging probs and alt earth via fixings was not good
     
  6. Mo younesi

    Mo younesi Member

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  7. Mo younesi

    Mo younesi Member

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    Here is the photos of both old and new alt connected. I only have the wires for the exciter and charging and don't have the rev counter.
     
  8. Mo younesi

    Mo younesi Member

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    Hello folks,
    It has taken me a couple of weekends to get here, but still haven't got to the bottom of the problem.
    Have now replaced the positive lead from the battery to the starter also have replaced the negative cable from the battery to the chassis and engine block making sure all contacts are grinned and clean, but still get only 12.2v when engine running across the battery terminal. I have measured from the positive stud on the alternator to the alternator body but reads only 12.2v. So I am almost now convinced that either the diodes in the brand new alternator are gone or the voltage regulator is gone.
    I wonder if anyone could kindly advise on the following. The white wire that usually gets connected to the rev counter of the alternator was not connected to the old alternator so months ago I traced it back though the engine loom and cut it, hence with the new alternator as seen in the pictures the white wire is missing. Would this effect the performance of the voltage regulator, should I connect it back ?
     
  9. steve2286w

    steve2286w Well-Known Member

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    Hopefully these fault finders might help
     

    Attached Files:

  10. Mo younesi

    Mo younesi Member

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    Many thanks Steve.
    Good news is that the ebay seller is sending me a brand new replacement alternator which should arrive in a couple of days time and am optimistic that once I put the new one on I will see that magic 14.4V number.
    The fault finding files will also be very handy for future issue so thank you for that.
    Regards,
    Mo
     
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  11. steve2286w

    steve2286w Well-Known Member

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    Result! Let us know if it solves the problem
     
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